It's because anything below 50" is completely and utterly a waste... Even for your kitchen. Go big or go home.
Oh, but just don't go too big because they only make plasmas in 65".
What 70" LCD?? I've never heard of any such thing!!
What to do if you find yourself stuck with no hope of rescue:
Consider yourself lucky that life has been good to you so far. Alternatively, if life hasn't been good to you so far, which given your present circumstances seems to be more likely, consider yourself lucky that it won't be troubling you much longer...
-- Excerpt from the Hitchhiker's Guide to the Galaxy.